Variable Volume Combustor with an Air Bypass System

ABSTRACT

The present application provides a combustor for use with flow of fuel and a flow of air in a gas turbine engine. The combustor may include a number of micro-mixer fuel nozzles positioned within a liner and an air bypass system position about the liner. The air bypass system variably allows a bypass portion of the flow of air to bypass the micro-mixer fuel nozzles.

This invention was made with government support under Contract No.DE-FC26-05NT42643 awarded by the U.S. Department of Energy. TheGovernment has certain rights in this invention.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTTECHNICAL FIELD

The present application and the resultant patent relate generally to gasturbine engines and more particularly relate to a variable volumecombustor with an air bypass system for improved turndown performance.

BACKGROUND OF THE INVENTION

Operational efficiency and the overall output of a gas turbine enginegenerally increases as the temperature of the hot combustion gas streamincreases. High combustion gas stream temperatures, however, may producehigher levels of nitrogen oxides and other types of regulated emissions.A balancing act thus exists between the benefits of operating the gasturbine engine in an efficient high temperature range while alsoensuring that the output of nitrogen oxides and other types of regulatedemissions remain below mandated levels. Moreover, varying load levels,varying ambient conditions, and many other types of operationalparameters also may have a significant impact on overall gas turbineefficiency and emissions.

Lower emission levels of nitrogen oxides and the like may be promoted byproviding for good mixing of the fuel stream and the air stream prior tocombustion. Such premixing tends to reduce combustion temperaturegradients and the output of nitrogen oxides. One method of providingsuch good mixing is through the use of a combustor with a number ofmicro-mixer fuel nozzles. Generally described, a micro-mixer fuel nozzlemixes small volumes of the fuel and the air in a number of micro-mixertubes within a plenum before combustion.

Although current micro-mixer combustors and micro-mixer fuel nozzledesigns provide improved combustion performance, the operability windowfor a micro-mixer fuel nozzle in certain types of operating conditionsmay be defined at least partially by concerns with dynamics andemissions. Specifically, the operating frequencies of certain internalcomponents may couple so as to create a high or a low frequency dynamicsfield. Such a dynamics field may have a negative impact on the physicalproperties of the combustor components as well as the downstream turbinecomponents. Given such, current combustor designs may attempt to avoidsuch operating conditions by staging the flows of fuel or air to preventthe formation of a dynamics field. Staging seeks to create local zonesof stable combustion even if the bulk conditions may place the designoutside of typical operating limits in terms of emissions, flammability,and the like. Such staging, however, may require time intensivecalibration and also may require operation at less than optimum levels.

There is thus a desire for improved micro-mixer combustor designs. Suchimproved micro-mixer combustor designs may promote good mixing of theflows of fuel and air therein so as to operate at higher temperaturesand efficiency but with lower overall emissions and lower dynamics.Moreover, such improved micro-mixer combustor designs may accomplishthese goals without greatly increasing overall system complexity andcosts.

SUMMARY OF THE INVENTION

The present application and the resultant patent thus provide acombustor for use with flow of fuel and a flow of air in a gas turbineengine. The combustor may include a number of micro-mixer fuel nozzlespositioned within a liner and an air bypass system positioned about theliner. The air bypass system variably allows a bypass portion of theflow of air to bypass the micro-mixer fuel nozzles.

The present application and the resultant patent further provide amethod of turning down a combustor for use with a flow of fuel and aflow of air in a gas turbine engine. The method may include the steps ofpositioning a number of micro-mixer fuel nozzles within a liner,positioning a number of air bypass holes through the liner, maneuveringthe micro-mixer fuel nozzles to open the air bypass holes in the liner,flowing a bypass portion of the flow of air away from the micro-mixerfuel nozzles, and reducing the flow of fuel to the micro-mixer fuelnozzles.

The present application and the resultant patent further provide an airbypass system for use with a flow of fuel and a flow of air incombustor. The air bypass system may include a number of micro-mixerfuel nozzles positioned within a cap assembly, the cap assemblypositioned within a liner, and a number of air bypass holes positionedabout the liner. The air bypass holes allow a bypass portion of the flowof air to bypass the micro-mixer fuel nozzles.

These and other features and improvements of the present application andthe resultant patent will become apparent to one of ordinary skill inthe art upon review of the following detailed description when taken inconjunction with the several drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a schematic diagram of a gas turbine engine showing a compressor,a combustor, and a turbine.

FIG. 2 is a schematic diagram of a combustor that may be used with thegas turbine engine of FIG. 1.

FIG. 3 is a schematic diagram of a portion of a micro-mixer fuel nozzlethat may be used with the combustor of FIG. 2.

FIG. 4 is a schematic diagram of a micro-mixer combustor as may bedescribed herein.

FIG. 5 is a perspective view of an example of the micro-mixer combustorof FIG. 4.

FIG. 6 is a side cross-sectional view of the micro-mixer combustor ofFIG. 5.

FIG. 7 is an expanded view of a portion of a nested fuel manifold systemas may be used with the micro-mixer combustor of FIG. 5.

FIG. 8 is a schematic view of the air bypass system as used with themicro-mixer combustor of FIG. 5 in a closed position.

FIG. 9 is a further schematic view of the air bypass system of FIG. 8 inan opened position.

DETAILED DESCRIPTION

Referring now to the drawings, in which like numerals refer to likeelements throughout the several views, FIG. 1 shows a schematic view ofgas turbine engine 10 as may be used herein. The gas turbine engine 10may include a compressor 15. The compressor 15 compresses an incomingflow of air 20. The compressor 15 delivers the compressed flow of air 20to a combustor 25. The combustor 25 mixes the compressed flow of air 20with a pressurized flow of fuel 30 and ignites the mixture to create aflow of combustion gases 35. Although only a single combustor 25 isshown, the gas turbine engine 10 may include any number of thecombustors 25. The flow of combustion gases 35 is in turn delivered to aturbine 40. The flow of combustion gases 35 drives the turbine 40 so asto produce mechanical work. The mechanical work produced in the turbine40 drives the compressor 15 via a shaft 45 and an external load 50 suchas an electrical generator and the like.

The gas turbine engine 10 may use natural gas, liquid fuels, varioustypes of syngas, and/or other types of fuels and combinations thereof.The gas turbine engine 10 may be any one of a number of different gasturbine engines offered by General Electric Company of Schenectady,N.Y., including, but not limited to, those such as a 7 or a 9 seriesheavy duty gas turbine engine and the like. The gas turbine engine 10may have different configurations and may use other types of components.Other types of gas turbine engines also may be used herein. Multiple gasturbine engines, other types of turbines, and other types of powergeneration equipment also may be used herein together.

FIG. 2 shows a schematic diagram of an example of the combustor 25 asmay be used with the gas turbine engine 10 described above and the like.The combustor 25 may extend from an end cover 52 at a head end to atransition piece 54 at an aft end about the turbine 40. A number of fuelnozzles 56 may be positioned about the end cover 52. A liner 58 mayextend from the fuel nozzles 56 towards the transition piece 54 and maydefine a combustion zone 60 therein. The liner 58 may be surrounded by aflow sleeve 62. The liner 58 and the flow sleeve 62 may define a flowpath 64 therebetween for the flow of air 20 from the compressor 15 orotherwise. Any number of the combustors 25 may be used herein in acan-annular array and the like. The combustor 25 described herein is forthe purpose of example only. Combustors with other components and otherconfigurations may be used herein.

FIG. 3 shows a portion of a micro-mixer fuel nozzle 66 that may be usedwith the combustor 25 and the like. The micro-mixer fuel nozzle 66 mayinclude a number of micro-mixer tubes 68 positioned about a fuel tube70. The micro-mixer tubes 68 generally may have substantially uniformdiameters and may be arranged in annular, concentric rows. Any number ofthe micro-mixer tubes 68 may be used herein in any size, shape, orconfiguration. The micro-mixer tubes 68 may be in communication with theflow of fuel 30 from the fuel tube 70 via a fuel plate 72 and the flowof air 20 from the compressor 15 via the flow path 64. A small volume ofthe flow of fuel 30 and a small volume of the flow of air 20 may mixwithin each micro-mixer tube 68. The mixed fuel-air streams may flowdownstream for combustion in the combustion zone 60 and used in theturbine 40 as described above. Other components and other configurationsmay be used herein.

FIG. 4 shows an example of a combustor 100 as may be described herein.The combustor 100 may be a micro-mixer combustor 110 with any number ofthe micro-mixer fuel nozzles 120 and the like positioned therein. Themicro-mixer fuel nozzles 120 may be similar to those described above.The micro-mixer fuel nozzles 120 may be sector shaped, circular shaped,and/or have any size, shape, or configuration. Likewise, the micro-mixernozzles 120 may include any number of micro-mixer tubes therein in anyconfiguration. The micro-mixer fuel nozzles 120 may be in communicationwith a common fuel tube 125. The common fuel tube 125 may carry one ormore fuel circuits therein. The multiple fuel circuits thus may allowstaging of the micro-mixer fuel nozzles 120. The micro-mixer fuelnozzles 120 may be mounted within a cap assembly 130 or a similarstructure. The cap assembly 130 may have any size, shape, orconfiguration. The cap assembly 130 may be surrounded by a conventionalseal 135 and the like.

Similar to that described above, the combustor 100 may extend from anend cover 140 at a head end 150 thereof A liner 160 may surround the capassembly 130 and the seal 135 with the micro-mixer fuel nozzles 120therein. The liner 160 may define a combustion zone 170 downstream ofthe cap assembly 130. The liner 160 may be surrounded by a case 180. Theliner 160, the case 180, and a flow sleeve (not shown) may define a flowpath 190 therebetween for the flow of air 20 from the compressor 15 orotherwise. The liner 160, the combustion zone 170, the case 180, and theflow path 190 may have any size, shape, or configuration. Any number ofthe combustors 100 may be used herein in a can-annular array and thelike. Other components and other configurations also may be used herein.

The combustor 100 also may be a variable volume combustor 195. As such,the variable volume combustor 195 may include a linear actuator 200. Thelinear actuator 200 may be positioned about the end cover 140 andoutside thereof The linear actuator 200 may be of conventional designand may provide linear or axial motion. The linear actuator 200 may beoperated mechanically, electro-mechanically, piezeo-electrically,pneumatically, hydraulically, and/or combinations thereof By way ofexample, the linear actuator 200 may include a hydraulic cylinder, arack and pinion system, a ball screw, a hand crank, or any type ofdevice capable of providing controlled axial motion. The linear actuator200 may be in communication with the overall gas turbine controls fordynamic operation based upon system feedback and the like.

The linear actuator 200 may be in communication with the common fueltube 125 via a drive rod 210 and the like. The drive rod 210 may haveany size, shape, or configuration. The common fuel tube 125 may bepositioned about the drive rod 210 for movement therewith. The linearactuator 200, the drive rod 210, and the common fuel tube 125 thus mayaxially maneuver the cap assembly 130 with the micro-mixer nozzles 120therein along the length of the liner 160 in any suitable position. Themultiple fuel circuits within the common fuel tube 125 may allow forfuel nozzle staging. Other components and other configurations also maybe used herein.

In use, the linear actuator 200 may maneuver the cap assembly 130 so asto vary the volume of the head end 150 with respect to the volume of theliner 160. The liner volume (as well as the volume of the combustionzone 170) thus may be reduced or increased by extending or retractingthe micro-mixer fuel nozzles 120 along the liner 160. Moreover, the capassembly 130 may be maneuvered without changing the overall systempressure drop. Typical combustor systems may change the overall pressuredrop. Such a pressure drop, however, generally has an impact on coolingthe components therein. Moreover, variations in the pressure drop maycreate difficulties in controlling combustion dynamics.

Changing the upstream and downstream volumes may result in varying theoverall reaction residence times and, hence, varying the overallemission levels of nitrogen oxides, carbon monoxide, and other types ofemissions. Generally described, reaction residence time directlycorrelates to liner volume and thus may be adjusted herein to meet theemission requirements for a given mode of operation. Moreover, varyingthe residence times also may have an impact on turndown and combustordynamics in that overall acoustic behavior may vary as the head end andthe liner volumes vary.

For example, a short residence time generally may be required to ensurelow nitrogen oxides levels at base load. Conversely, a longer residencetime may be required to reduce carbon monoxide levels at low loadconditions. The combustor 100 described herein thus provides optimizedemissions and dynamics mitigation as a tunable combustor with novariation in the overall system pressure drop. Specifically, thecombustor 100 provides the ability to vary actively the volumes hereinso as to tune the combustor 100 to provide a minimal dynamic responsewithout impacting on fuel staging.

Although the linear actuator 200 described herein is shown asmaneuvering the micro-mixer fuel nozzles 120 in the cap assembly 130 asa group, multiple linear actuators 200 also may be used so as tomaneuver individually the micro-mixer fuel nozzles 120 and to providenozzle staging. In this example, the individual micro-mixer fuel nozzles120 may provide additional sealing therebetween and with respect to thecap assembly 130. Rotational movement also may be used herein. Moreover,non-micro-mixer fuel nozzles also may be used herein and/ornon-micro-mixer fuel nozzles and micro-mixer fuel nozzles may be usedtogether herein. Other types of axial movement devices also may be usedherein. Other component and other configurations may be used herein.

FIG. 5 and FIG. 6 show an example of a pre-nozzle fuel injection system220 that may be used with the combustor 100 and the like. Each of thefuel nozzles 120 may be mounted onto the pre-nozzle fuel injectionsystem 220. The pre-nozzle fuel injection system 220 may include a fuelnozzle manifold 230. The fuel nozzle manifold 230 may be incommunication with the common fuel tube 125 and may be maneuverable viathe drive rod 210 as described above. The fuel nozzle manifold 230 mayhave any size, shape, or configuration.

The fuel nozzle manifold 230 of the pre-nozzle fuel injection system 220may include a center hub 240. The center hub 240 may have any size,shape, or configuration. The center hub 240 may accommodate a number ofdifferent flows therein. The fuel nozzle manifold 230 of the pre-nozzlefuel injection system 220 may include number of support struts 250extending from the center hub 240. Any number of the support struts 250may be used. The support struts 250 may have a substantiallyaerodynamically contoured shape 255 although any size, shape, orconfiguration may be used herein. Specifically, each of the supportstruts 250 may include an upstream end 260, a downstream end 270, afirst sidewall 280, and a second sidewall 290. The support struts 250may extend radially from the center hub 240 to the cap assembly 130.Each support strut 250 may be in communication with one or more of thefuel nozzles 120 so as to provide the flow of fuel 30 thereto. The fuelnozzles 120 may extend axially from the downstream end 270 of each ofthe support struts 250. Other components and other configurations may beused herein.

FIG. 7 shows a nested fuel manifold system 320 as may be describedherein. The nested fuel manifold system 320 may cooperate with thepre-nozzle fuel injection system 220 or other type of fuel injectionsystem so as to deliver safely one or more flows of fuel 30 to the fuelnozzles 120. Moreover, the nested fuel manifold system 320 also maycooperate with the linear actuator 200 and the drive rod 210 toaccommodate the axial movement of the fuel nozzles 120 within the capassembly 130 while limiting the number of penetrations through the endcover 140.

The nested fuel manifold system 320 includes a nested fuel manifold 330.The nested fuel manifold 330 may be positioned about the linear actuator200 outside of the end cover 140 at the head end 150 for movementtherewith. The nested fuel manifold 330 may include a number of fuelcircuit connections 340. Any number of the fuel circuit connections 340may be used. The fuel circuit connections 340 may be in communicationwith the same or different types of flows of fuel 30 so as to providefuel flexibility herein. The fuel circuit connections 340 may have anysize, shape, or configuration.

Each of the fuel circuit connections 340 of the nested fuel manifold 330may be in communication with a nested fuel supply circuit 350. In thisexample, three (3) nested fuel supply circuits 350 are shown: a firstnested fuel supply circuit 360, a second nested fuel supply circuit 370,and a third nested fuel supply circuit 380. Any number of the nestedfuel supply circuits 350, however, may be used herein. The nested fuelsupply circuits 350 may be annularly nested within each other such thatthe first nested fuel supply circuit 360 is positioned within the secondnested fuel supply circuit 370 which, in turn, is positioned within thethird nested fuel supply circuit 380. A fuel feed seal 390 may separateeach of the nested fuel supply circuits 350. Each of the nested fuelsupply circuits 350 may take the form of a flexible hose and the like.The nested fuel supply circuits 350 may have any size, shape, orconfiguration. The nested fuel supply circuits 350 collectively act asthe common fuel tube 125. Other components and other configurations maybe used herein.

FIGS. 8 and 9 show an example of an air bypass system 800 that may beused with the combustor 100 and the like. The air bypass system 800 mayinclude a number of air bypass holes 810 positioned through the liner160. The air bypass holes 810 may be positioned through the liner 160about an aft end 820 of the cap assembly 130. The air bypass holes 810may be positioned in a single row 830 or a number of rows 830 may beaxially arranged so as to provide staging. The air bypass holes 810 mayhave any size, shape, or configuration. Air bypass holes 810 ofdifferent sizes, shapes, and configurations may be used together hereinin any orientation. Any number of the air bypass holes 810 may be usedherein. Other components and other configurations may be used herein.

In this example, the seal 135 on the cap assembly 130 may be in the formof a hula seal 840 and the like. Generally defined, the hula seal 840may be a finger seal or a leaf spring used to seal a sliding interfaceor an annular gap between two concentric ducts. Other types of seals 135and sealing mechanism may be used herein. Any number of the hula seals840 may be used herein in any size, shape, or configuration. The hulaseals 840 may be positioned about the aft end 820 of the cap assembly130. Such positioning avoids potential damage to a thermal barriercoating 850 and the like on the hot surface of the liner 160. Othercomponents and other configurations may be used herein.

FIG. 8 shows the air bypass system 800 in a closed position 860.Specifically, when the cap assembly 130 is advanced in a downstreamdirection within the liner 160, the hula seals 840 prevent the flow ofair 20 therethrough. FIG. 9 shows the air bypass system in an openposition 870. In this position, the hula seals 840 are upstream of theair bypass holes 810 when the cap assembly 130 is retracted to a fullaft position 880. The full aft position 880 provides the largestcombustor volume and, hence, the longest residence time. With the airbypass holes 810 open, a bypass portion 890 of the flow of air 20 mayflow therethrough and bypass the fuel nozzles 120. The air bypass holes810 may be configured to allow a predetermined volume of the bypassportion 890 to flow therethrough.

The use of the bypass portion 890 of the flow of air 20 allows for lessof the flow of fuel 30 to be provided to the fuel nozzles 120. The airbypass system 800 thus allows for the combustor 100 to be turned down toa much lower point while maintaining the same fuel to air ratio to thefuel nozzles 120 for stable flame performance. Moreover, the air bypasssystem 800 may improve overall emissions compliance by dumping thebypass portion 890 away from the center nozzle so as to control theformation of carbon monoxide. The hula seals 840 also may be positionedsuch that only a predetermined number of the bypass holes 810 may beopen so as to vary the volume of the bypass portion 890 and, hence, soas to vary the fuel to air ratio to the fuel nozzles 120. The air bypasssystem 800 may precisely control the volume of the bypass portion 890 byvarying the position of the hula seals 840 and the cap assembly 130 viathe linear actuator 200. The air bypass system 800 thus may have anynumber of partially open positions with the hula seals 840 upstream ofsome of the air bypass holes 810.

The air bypass system 800 thus provides the combustor 100 with improvedturn down performance without the use of addition components for anoverall robust system. The air bypass system 800 allows for furtherturndown, emissions compliance, and dynamics mitigation. The combustor100 thus may operate within required parameters at relatively low loads.

It should be apparent that the foregoing relates only to certainembodiments of the present application and the resultant patent.Numerous changes and modifications may be made herein by one of ordinaryskill in the art without departing from the general spirit and scope ofthe invention as defined by the following claims and the equivalentsthereof.

We claim:
 1. A combustor for use with a flow of fuel and a flow of airin a gas turbine engine, comprising: a plurality of micro-mixer fuelnozzles; the plurality of micro-mixer fuel nozzles positioned within aliner; and an air bypass system positioned about the liner; the airbypass system variably allowing a bypass portion of the flow of air tobypass the plurality of micro-mixer fuel nozzles.
 2. The combustor ofclaim 1, wherein the plurality of micro-mixer fuel nozzles comprises aplurality of micro-mixer fuel tubes and a fuel plate.
 3. The combustorof claim 1, wherein the air bypass system comprises a plurality of airbypass holes through the liner.
 4. The combustor of claim 3, wherein theplurality of air bypass holes is configured in a row.
 5. The combustorof claim 3, wherein the plurality of air bypass holes is configured in aplurality of rows.
 6. The combustor of claim 1, wherein the plurality ofmicro-mixer fuel nozzles is positioned within a cap assembly.
 7. Thecombustor of claim 6, wherein the cap assembly comprises a sealpositioned about the liner.
 8. The combustor of claim 6, wherein theseal is positioned about an aft end of the cap assembly.
 9. Thecombustor of claim 6, wherein the air bypass system comprises a closedposition with the seal downstream of the air bypass system.
 10. Thecombustor of claim 6, wherein the air bypass system comprises an openposition with the seal upstream of the air bypass system.
 11. Thecombustor of claim 10, wherein the open position comprises the capassembly in a full aft position.
 12. The combustor of claim 6, whereinthe air bypass system comprises a partially opened position with theseal partially upstream of the air bypass system.
 13. The combustor ofclaim 6, wherein the seal comprises a hula seal.
 14. The combustor ofclaim 1, further comprising a linear actuator to maneuver the pluralityof micro-mixer fuel nozzles within the liner.
 15. A method of turningdown a combustor for use with a flow of fuel and a flow of air in a gasturbine engine, comprising: positioning a plurality of micro-mixer fuelnozzles within a liner; positioning a plurality of air bypass holesthrough the liner; maneuvering the plurality of micro-mixer fuel nozzlesto open the air bypass holes in the liner; flowing a bypass portion ofthe flow of air away from the plurality of micro-mixer fuel nozzles; andreducing the flow of fuel to the plurality of micro-mixer fuel nozzles.16. An air bypass system for use with a flow of fuel and a flow of airin combustor, comprising: a plurality of micro-mixer fuel nozzles; theplurality of micro-mixer fuel nozzles positioned within a cap assembly;the cap assembly positioned within a liner; and a plurality of airbypass holes positioned about the liner; the air bypass holes allowing abypass portion of the flow of air to bypass the plurality of micro-mixerfuel nozzles.
 17. The air bypass system of claim 16, wherein the capassembly comprises a seal positioned about an aft end thereof.
 18. Theair bypass system of claim 17, wherein the air bypass system comprises aclosed position with the seal downstream of the air bypass holes. 19.The air bypass system of claim 17, wherein the air bypass systemcomprises an open position with the seal upstream of the air bypassholes.
 20. The air bypass system of claim 17, wherein the seal comprisesa hula seal.